The present invention relates to a bearing device such as a hub unit mounted to a vehicle such as an automobile for example, and to a method for measuring an axial force of the bearing device.
In a conventional hub unit for a vehicle, a rolling bearing of an angular contact type is attached to an outer periphery of a hub wheel, a cylindrical shaft end of the hub wheel is bent diametrically outward by rotary forging and caulked on an end face of an inner ring of the rolling bearing, thereby applying a pre-load to the rolling bearing and preventing the rolling bearing from loosening from the hub unit.
When the caulking operation is carried out, in order to inhibit a caulking force from being applied to the inner ring of the rolling bearing and to inhibit a raceway of the inner ring from being deformed, an annular support jig is used.
When the shaft end of the hub wheel is bent and caulked in the diametrically outward direction, this support jig restrains an outer periphery of a shoulder portion of the inner ring to inhibit the inner ring from being deformed.
This support jig is necessary for improving the performance of the hub unit, but it is troublesome to insert the support jig between the opposed inner ring and outer ring of the rolling bearing so as to bring the support jig into abutment against the outer periphery of the inner ring shoulder portion.
Moreover, even if the inner ring shoulder portion is restrained by the support jig, since the inner ring can be deformed by the rotary forging in this structure, it is necessary to carry out, with high precision, the rotary forging operation itself, therefore and there is a limit for increasing the speed of the operation thereof. For this reason, the conventional hub unit structure is inferior in mass production performance.
Accordingly, it is an object of the present invention to provide a bearing device suitable for mass production and in which the number of assembling steps and assembling time are reduced by making the inner ring such that it is less prone to be deformed so that the precision of the bearing is not affected even if a support jig is not used.
It is another object of the present invention to provide a method for measuring an axial force of the bearing device which can be assembled without using the support jig and which was assembled without restraining the inner ring using the support jig.
Other objects, features and advantages will be apparent from the following description.
According to the first embodiment of the invention, there is provided a bearing device comprising a shaft body having a shaft end formed into a cylindrical shape as a caulking portion; and an angular contact type rolling bearing fitted over an outer periphery of the shaft body; wherein an axially outer edge of an inner ring of the rolling bearing is partially chamfered roundly with a predetermined radius of curvature, the caulking portion comprises a large-diameter portion having an outer diameter substantially coinciding with an inner diameter of an inner periphery of the inner ring and fitted to the inner periphery of the inner ring, and a small-diameter portion having an outer diameter smaller than the inner diameter of the inner ring and extended axially in one axial direction from the large-diameter portion through a predetermined distance, a starting point of the small-diameter portion is located closer to an axially central portion than a chamfer-starting point of the axially outer edge of the inner ring, and the small-diameter portion of the caulking portion is bent diametrically outward and caulked on an end face of the inner ring of the rolling bearing so as to prevent the rolling bearing from falling out from the bearing device and to apply a pre-load to the rolling bearing.
According to the first embodiment of the invention, since the small-diameter portion is smaller than the inner diameter of the inner ring, when it is subjected to a rotary forging using a forging tool for example, a force for deforming the inner ring diametrically outward is not applied to the inner ring. In this state, since the starting point of the small-diameter portion is located closer to the axially central portion than the chamfer-starting point of the axially outer edge of the inner ring, when it is subjected to a rotary forging using a forging tool for example, the small-diameter portion is deformed diametrically outward such that it is extended in the vicinity of the starting point.
When the outer periphery of the small-diameter portion came into contact with the axially outer edge of the inner ring, the force for deforming the inner ring diametrically outward became smaller, a deforming force for deteriorating the circularity of the inner ring is not applied to the inner ring, and as a result, the inner ring is not deformed, and the caulking portion is caulked on the end face of the inner ring as a caulked portion.
From the above reason, according to the first embodiment of the invention, the support jig is unnecessary and thus, the number of assembling steps and assembling time are reduced, and the structure of the hub unit is suitable for mass production.
Preferably, in the first embodiment of the invention, the shaft body is a wheel hub to which a wheel is mounted, the wheel hub having a shaft portion comprising a small-diameter outer peripheral face and a large-diameter outer peripheral face, a shaft end of the shaft portion is the caulking portion, the rolling bearing is a double row angular contact ball bearing having an inner ring of a single raceway fitted over the small-diameter outer peripheral face of the shaft portion of the wheel hub, a single outer ring having two row raceway grooves, a plurality of balls arranged in two rows, and two crown-shaped retainers, the large-diameter outer peripheral face of the shaft portion of the wheel hub is one inner ring, the axially outer edge of the inner ring of the rolling bearing is partially chamfered roundly with a predetermined radius of curvature, and the small-diameter portion of the caulking portion is bent diametrically outward and caulked on an end face of the inner ring of the rolling bearing so as to prevent the rolling bearing from falling out from the bearing device and to apply a pre-load to the rolling bearing.
Further, in the first embodiment of the invention, it is preferable that the small-diameter portion of the caulking portion includes, before the small-diameter portion is caulked, a junction having a tapered face which is reduced in diameter in one axial direction from a starting point of the small-diameter portion, and a shaft end extending in one axial direction from the junction. In this case, the small-diameter portion can smoothly extend along an inner periphery of the inner ring in a state in which the small-diameter portion is not in contact with the inner periphery of the inner ring, and it is effective to prevent the inner ring from being warped by the caulking.
It is preferable that in the first embodiment of the invention, an outer diameter difference between the large-diameter portion and the small-diameter portion of the caulking portion before the small-diameter portion is caulked is 0.1 mm or less. This is preferable because the small-diameter portion can be caulked in a state in which the small-diameter portion is tightly connected to the inner ring without a gap in the caulked state.
According to a second invention, there is provided a bearing device comprising a shaft body whose shaft end is formed into a cylindrical shape as a caulking portion; and an angular contact type rolling bearing fitted over an outer periphery of the shaft body; wherein a counter bore-opposite side shoulder portion in an inner ring of the rolling bearing is provided with a swelling portion which extends diametrically outward with respect to a standard specification product, a thickness of the counter bore-opposite side shoulder portion in the diametrical direction is increased by the swelling portion, the caulking portion of the shaft body is bent diametrically outward and caulked on a counter bore-opposite side end face of the inner ring of the rolling bearing so as to prevent the rolling bearing from falling out from the bearing device and to apply a pre-load to the rolling bearing.
According to the second embodiment of the invention, since the volume of the counter bore-opposite side end face is increased and the section modulus is increased, the rigidity of the counter bore-opposite side end face is increased.
When the forging tool is rolled to bend and deform the caulking portion diametrically outward and the caulking portion is caulked on the end face of the counter bore-opposite side end, the caulking force is applied to the counter bore-opposite side end of the inner ring. In this case since the counter bore-opposite side end has a great rigidity, it is not deformed by the caulking. Therefore, the raceway of the inner ring is not deformed by the caulking and thus, the circularity of the raceway is maintained, and the precision of the bearing is maintained.
Further, the counter bore-opposite side end is not deformed by the caulking, a tensile stress in the circumferential direction is not applied to the raceway of the inner ring by the caulking and as a result, fatigue of the bearing is reduced and the life span is not shortened by the caulking.
Further, since the thickness of the entire inner ring is not set thick, it is unnecessary to reduce the inner diameter of the inner ring. Therefore, the inner ring can be caulked without deforming the inner ring while maintaining the strength of the shaft.
From the above reason, according to the second embodiment of the invention, the support jig is unnecessary and thus, the number of assembling steps and assembling time are reduced, and the structure of the hub unit is suitable for mass production.
According to a third embodiment of the invention, there is provided an axial force measuring method including a preparing process and an actually working process, the preparing process comprises, a first preparing step for measuring an initial axial size of the bearing device before it is caulked, a second preparing step for varying an axial force applied to the rolling bearing to measure an axial size at that time, and a third preparing step for obtaining a deviation (a variation amount of the axial size) between the initial axial size measured in the first preparing step and a result of measurement in the second preparing step, thereby producing correlation data between the axial force and the variation amount of axial size, and the actually working process comprises a first actually working step for measuring an actually working axial size of the bearing device after it is caulked, a second actually working step for obtaining a deviation (a variation amount of the axial size) between the actually working axial size in the first actually working step and the initial axial size, and a third actually working step for collating the obtained variation amount of the axial size and the correlation data to recognize an axial force.